This invention relates to heat absorbing apparatus and more particularly to an improved solar energy collector for heating a heat transfer fluid with infrared energy from the sun.
With the growing emphasis on energy conservation, collectors for solar energy have received increasing attention. Of the numerous collectors which are presently available, two of the more efficient types involve metal tube heat absorbers through which a heat transfer fluid such as water is circulated. In each case, the heat absorber is disposed within an enclosing glass tube, and there is a region of vacuum, or of reduced pressure, within the enclosing glass tube. In one case, the region within the enclosing glass tube is hermetically sealed, and the entire interior of the enclosing glass tube is the vacuum region. In another case, there is a second enclosing glass tube, and the region between the two glass tubes in the vacuum region. The former structure is somewhat more efficient than the latter, and somewhat more expensive, because of the necessity for hermetically sealing between the heat absorber and the surrounding glass tube. In both embodiments, the vacuum region greatly increases the efficiency of the solar energy collector by reducing convection and conduction heat losses from the heat absorber.
The efficiency of the solar energy collector is sometimes increased by positioning a reflecting surface to direct energy on the heat absorbers. In the past, the reflecting surface has been positioned at a fixed angle determined by the location of the solar energy collector on the earth. The reflector has a maximum efficiency only during a short time interval in each day as the sun moves across the sky.